USPTO Patents Application 10537760

(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)

(19) World Intellectual Property Organization
International Bureau

(43) International Publication Date
28 June 2001 (28.06.2001)

111

PCT

(10) International Publication Number

WO 01/45829 Al

(51) International Patent Classification 7 : B01D 65/10,
G01N 15/08

(21) International Application Number: PCT/CA00/01461

(22) International FilingDate: 6 December 2000 (06. 12.2000)

(25) Filing Language: English

(26) Publication Language: English

(30) Priority Data:

09/468,779

21 December 1999 (21.12.1999) US

(71) Applicant (for all designated States except US): ZENON
ENVIRONMENTAL INC. [CA/CA]; 3239 Dundas Street
West, Oakville, Ontario L6M4B2 (CA).

(72) Inventors; and

(75) Inventors/Applicants (for US only): COTE, Pierre
[CA/CA]; 26 TaUy-Ho Drive, Dundas, Ontario L9H 3M6
(CA). JANSON, Arnold [CA/CA]; 343 Rankin Drive,
Burlington, Ontario L7N 2B2 (CA). ADAMS, Nicholas
[CA/CA]; 37 Kipling Road, Hamilton, Ontario L8S 3X2
(CA).

(74) Agent: BERESKIN & PARR; 40 King Street West, 40th
Floor, Toronto, Ontario M5H 3Y2 (CA).

(81) Designated States (national): AE, AG, AL, AM, AT, AU,
AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CR, CU, CZ,
DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR,
HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR,
LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ,
NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM,
TR, IT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW.

(84) Designated States (regional): ARIPO patent (GH, GM,
KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), Eurasian
patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), European
patent (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE,
IT, LU, MC, NL, PT, SE, TR), OAP1 patent (BF, BJ, CF,
CG, Ct, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG).

Published:

— With international search report.

For two-letter codes and other abbreviations, refer to the "Quid-
ance Notes on Codes and Abbreviations" appearing at the begin-
ning of each regular issue of the PCT Gazette.

Q\ (54) Title: METHOD AND APPARATUS FOR TESTING THE INTEGRITY OF FILTERING MEMBRANES
<N

^ (57) Abstract: An improvement to an outside/in hollow fibre membrane filtration system includes a source of suction on the lumens
^ of the membranes or pressure on the outside of the membranes operable without producing permeate and an air collector to collect
^--j any air that passes from the outside of the membranes to their lumens during an integrity test. A method for testing the integrety of
^ filtering membranes involves exposing a first side of the membranes to air while a second side of the membranes remains exposed to
water. A transmembrane pressure forces air through defects of concern in the membranes. Air that passes through a set of membranes
Q is collected and its amount measured and compared to an acceptable amount of air to indicate whether there is a defect in the set
^ of membranes. Preferably, air is collected individually from a plurality of membrane units in a filtration train and the amounts so
^ collected compared to indicate if one of the membrane units is defective.

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Title: Method and Apparatus for Testing the Integrity of Filtering
Membranes

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for testing
5 the integrity of filtering membranes.

BACKGROUND OF THE INVENTION

Filtering membranes are used to permeate a relatively particle free
liquid from a liquid rich in particles. Reverse osmosis and nanofiltration
membranes, for example, are used to produce very high quality water for
10 drinking or industrial applications. Ultrafiltration and microfiitration
membranes are used at lower pressure to filter water for drinking or
industrial applications and to treat waste water.

One reason for using membranes to filter water is that membranes
are able to remove very small particles including pathogenic

15 microorganisms and colloids. Thus, strong chemicals may not be required
as a primary disinfectant in drinking water applications and a nearly
complete lack of colloids in water produced for industrial purposes
improves the performance of many industrial processes. To ensure that
undesired particles are removed, however, the integrity of a membrane unit

20 must be monitored and tested regularly. In particular, although membranes
are usually tested after they are manufactured, leaks can develop when the
membranes are installed in a filtering system and during the subsequent
operation of the system. For example, leaks may result from fatigue, from
over-pressurization, or from cleaning and maintenance activities.

25 Membrane integrity can be monitored using continuous or

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discontinuous methods. Continuous integrity testing techniques, which
include particle counting and acoustic analysis, do not evaluate the
membrane itself but instead monitor and assess a surrogate parameter to
diagnose the membrane condition. For instance, a batch or on-line particle
5 counter generally includes a light scattering sensor, typically laser-based,
interfaced with a computer running particle enumeration software that
assesses the number of particles in one or more particle size ranges: see
generally Panglish et al M "Monitoring the Integrity of Capillary Membranes by
Particle Counters", Desalination, vol. 119, p. 65-72 (1998). Similarly, a

10 particle monitor that measures the fluctuation in intensity in a narrow light
beam transmitted through a permeate sample is also known. Through
subsequent computer analysis, the observed fluctuations can be converted
into an index of water quality. Particle counting and particle monitoring
techniques require elaborate and expensive measurement equipment that

15 is subject to measurement drift, noise, and periodic maintenance such as
calibration. In addition, these methods generally do not differentiate
between undesirable particles and other signals that have no relation to
membrane integrity, particularly air bubbles produced on the permeate side
of the membrane and associated with backwashing operations. Moreover,

20 the number of membrane units or modules that can be simultaneously
monitored using these integrity testing methods is limited by dilution effects.

In acoustic membrane analysis methods, as described in Glucina et
al., "Acoustic Sensor; a Novel Technique for Low Pressure Membrane
Integrity Monitoring", AWWA Membrane Conference, Long Beach, California
25 (February 28 to March 3, 1999), one or more sound wave sensors or
transducers are placed on a membrane unit to detect anomalies in the
acoustic response of the membrane, namely noise originating from broken
fibres. These acoustic techniques, however, detect only broken fibres and
do not detect more subtle defects in, or the general deterioration of, a

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membrane. Furthermore, these methods are susceptible to interference
from surrounding noise and are very expensive, since they require at least
one acoustic sensor per membrane unit and each of these sensors must
be electrically connected to a central computer for appropriate signal
5 analysis.

In another class of integrity testing techniques, membrane integrity is
assessed directly while permeation is temporarily stopped. Typically, air
(or another suitable gas) is applied to a first side of a wet membrane at a
pressure higher than the pressure of water or air on a second side of the

10 membrane to create a trans-membrane pressure but at a pressure lower
than the bubble point of a membrane without defects. A rapid flow of air
from the first side of the membrane to the second side indicates a leak in
the membrane. Such integrity testing methods are often referred to as air
leak tests and examples are discussed in United States Patent No.

15 5,353,630 to Soda et al. and in International Patent Application No.
PCT/FR97/00930 (corresponding to International Publication No. WO
97/45193) assigned to OTV Omnium de Traitements et de Valorisation of
France. In United States Patent No. 5,353,630, the water on the feed side of
a shelled membrane module is replaced with pressurized air. In

20 International Patent Application No. PCT/FR97/00930, the feed side of an
immersed, unshelled membrane module is exposed to air at atmospheric
pressure by emptying a tank in which the module is immersed and then a
partial vacuum is applied to the filtered water on the permeate side of the
module.

25 In air leak tests, the trans-membrane pressure used is selected to

exceed the bubble point corresponding to defects or holes whose size is of
interest, i.e. whose undesirable passage requires monitoring. The bubble
point is the air pressure which exceeds the surface tension of a liquid in a

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hole of the relevant size. The bubble point is described theoretically by the
Young Laplace equation which provides the pressure difference required
across a curved interface in terms of the surface or interfacial tension and
the principal radii of curvature. For example, pressures of 0.3 to 1.0 bar are
5 used to detect holes in the range of 0.5 to 2.3 |jm.

In different air leak test methods, the trans-membrane pressure is
controlled over time according to alternate strategies to provide an indication
of the size or number of leaks. For example, in a pressure hold test ("PHT"),
the flow rate of air required to maintain a certain trans-membrane test
10 pressure is measured. In a pressure decay test ("PDT"), the rate of trans-
membrane pressure change (decay) from an initial value is measured.
With both tests, measured values are compared to membranes known to
be free from defects. Both tests require precise air flow or air pressure
sensors or both and are accordingly expensive to install.

15 Another problem with the PHT and PDT is that the accuracy of both

tests is limited by the fact that air crosses the membrane by diffusion
through water filled pores in addition to flowing through defects in the
membrane. Such diffusive air flow is related to the surface area of the
membrane unit being tested. In a large membrane unit (ie. with a flow

20 capacity in the range of a thousand or more cubic metres per day), the
diffusive air flow may be similar in magnitude to the air flow expected from a
defect of the size being tested for. This problem makes detecting a single
broken fibres difficult in a membrane unit of this size and generally limits the
size of membrane units that can be properly tested with such tests. Thus, in

25 a large municipal or industrial installation with several large membrane
units connected together in a filter train, several distinct sets of membrane
integrity testing apparatus are required. Thus, there is a need for an
improved method and system for accurately measuring the integrity of

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filtering membranes.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and
apparatus for providing an integrity test for filtering membranes. This object
5 is met by the combination of features, steps or both found in the
independent claims, the dependent claims disclosing further advantageous
inventions. The following summary may not describe all necessary features
of the invention which may reside in a sub-combination of the following
features or in a combination with features described in other parts of this
10 document.

One aspect of the present invention is a method and system for
testing the integrity of membranes used to filter a liquid feed to produce a
liquid permeate. A gas such as air is applied to the feed side of the
membranes and subjected to a trans-membrane pressure towards the

15 permeate side of the membranes which remains in contact with liquid
permeate. The air that crosses a membrane locally (i.e. on a specific unit of
membranes) into the liquid permeate is separated from the liquid permeate
and collected. The volume of air collected for each membrane unit tested
provides a quantified indication of the integrity of the membrane unit, since

20 that volume is directly related to the amount and quality of leaks in the
membrane unit.

In another aspect, the invention is directed at an improvement to an
outside/in hollow fibre filtration system. For some systems, particularly
those with immersed shell-less membrane units, the improvement
25 includes a source of suction on the lumens of the membranes operable
without producing permeate, such as a permeate pump operating in a

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recycle loop. For other systems, particularly those with shelled modules,
the improvement includes a source of pressure on the outside of the
membranes operable in the absence of water on the outside of the
membranes, such as pressurized air. In both cases, an air collector is also
5 provided at a high point in a permeate pipe to collect any air that passes
from the outside of the membranes to their lumens during an integrity test.
The amount of air so collected is measured and then released prior to
subsequent tests.

In another aspect, the invention is directed at a method for testing the

10 integrity of filtering membranes used to filter a liquid feed to produce a liquid
permeate. After stopping filtration, a feed side of the membranes is
exposed to air while a permeate side of the membranes remains exposed
to the liquid permeate. A selected transmembrane pressure is created
across the membranes from the feed side of the membranes to the

15 permeate side for a selected period of time, the selected transmembrane
pressure being sufficient to force air through a potential defect of concern in
the membranes. The feed side of the membranes is then re-exposed to
water and permeation is resumed. Air that passed through a set of
membranes into the liquid permeate is separated and collected and its

20 amount measured. The set of membranes is chosen to produce a
membrane unit of such a size that a defect of interest is distinguishable
from diffusion of air through the pores of the membranes in the membrane
unit. The amount of air collected from the membrane unit is related to an
acceptable amount of air to indicate whether there is a defect in the

25 membranes of the membrane unit. Preferably, air is collected individually
but simultaneously from a plurality of membrane units in a filtration train.
The amount of air collected from a membrane unit is compared with the
amount of air collected from another membrane unit to indicate if one of the
membrane units is defective after the pressure on the permeate side of the

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membrane units is equilibrated.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described below with reference
to the following drawings:

5 Figure 1 illustrates integrity testing apparatus for immersed shell-

less outside-in flow membranes with certain components shown in
elevation view.

Figure 2 illustrates integrity testing apparatus according to the
embodiment of Figure 1 with certain components shown in plan view.

10 Figure 3 illustrates integrity testing apparatus for an outside-in flow

membrane module in a pressurized shell.

Figures 4, 5 and 6 illustrate cross sections of membranes showing
water in or around the pores during an integrity test.

DETAILED DESCRIPTION OF THE INVENTION

15 Referring to Figures 1 through 3, the embodiments described below

involve hollow-fibre filtering membranes 10 which may be made of
polypropylene, polysulfone derivatives, or the like. In Figure 1 through 3, the
membranes 10 are used in an outside-in ("O/l") mode. In the O/l mode,
feed water 12 is applied to the outside of the membranes 10 and permeate

20 14 is collected from the lumens of the membranes 10. Although the
description below refers to filtering water, the present invention is applicable
to integrity tests of membranes used for filtering other liquids.

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Referring to Figures 1 and 2, a plurality of membranes 10 (typically
thousands) are assembled into a submerged membrane unit 16. A plurality
of membrane units 16, collectively referred to as a filtration train 17, are
immersed into a tank 18 and connected by permeate collection pipes 20
5 and an isolation valve 22 to a header 24, a permeate pump 26, an outlet
valve 28 and an outlet 30. Feed water 12 enters the tank 18 through a feed
valve 32. Permeation is performed by operating the permeate pump 26 to
create a negative pressure in the lumens of the membranes 10. Permeate
14 is drawn out of the tank 18 through the membranes 10 and replaced by
10 feed water 12 such that the membranes 10 remain immersed. From time to
time, a permeate storage valve 52 is opened to admit permeate 14 to a
storage tank 54. A backwash loop 50 has backwash valves 60 to allow the
permeate pump 26 to draw permeate 14 from the storage tank 54 and flow it
through the membranes 10 is a reverse direction.

15 To facilitate an integrity test, an air collector 33 is provided at a high

point in the permeate collection pipes 20 such that air entrained in
permeate 14 will collect in the air collector 33. The air collector 33 has a
collection vessel 34, an air release valve 36 (also referred to as a priming
valve) and a check valve 38. The bottom of the collection vessel 34 is in fluid

20 communication with the flow of permeate 14 in the permeate collection
pipes 20. The top of the collection vessel is in fluid communication with the
atmosphere through the air release valve 36 and check valve 38. The
collection vessel 34 is preferably a clear cylinder with graduations allowing
a visual determination of volume. Optionally, the collection vessel may have

25 a pressure gauge or sensor (not shown) and a level sensor (not shown) to
allow the volume and pressure of air in the collection vessel 34 to be
determined remotely or automatically by a programmable logic controller.
Air release valve 36 allows air to leave the collection vessel 34 when it is

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under pressure while check valve 38 prevents air from entering the air
collection vessel 34 from the atmosphere generally when the air collection
vessel 34 is under vacuum. In place of the air release valve 36 and check
valve 38, a solenoid valve and vacuum pump can be used to remove air
5 from the collection vessel 34 when required. If so, a single vacuum pump is
preferably connected by a header to a plurality of air collection vessels 34
each having its own associated solenoid valve.

Also provided is a recycle loop 40 having a loop inlet 46, a loop outlet
48, loop closure valves 42 and a loop tank 44. The loop inlet 46 is located at

10 the discharge side of the permeate pump 26 and the loop outlet is located
at the inlet side of the permeate pump 26. Thus the permeate pump 26 can
be operated to produce a vacuum in the lumens of the membranes 10
without producing permeate 14. In many cases, the ordinary permeate
pump 26 may not produce sufficient vacuum without cavitation or the cost of

15 operating the permeate pump 26 to test the membranes exceeds the cost of
purchasing a separate vacuum pump for testing the membranes. In these
cases, it would be preferably to include a valve operable to disconnect the
permeate pump 26 from the header 24 and connect instead a separate
vacuum pump (with necessary apparatus) or other apparatus suitable for

20 producing a vacuum without flow of permeate 14.

To perform an integrity test, the following steps are performed:

1. Permeation is stopped by stopping the permeate pump 26.

2. Any air (from degassing as a result of the drop in pressure across
the membrane etc.) in the collection vessel 34 is discharged. This may be

25 done by backwashing the filtration train 17 at a pressure that exceeds the
minimum pressure at which the air release valve 36 will vent the collection

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vessel 34, by opening a solenoid valve during backwash (if one is used in
place of the air release valve 36) or by opening a solenoid valve and
operating a vacuum pump to overcome the suction of the permeate pump
26 during permeation. The latter method is preferred in systems where
5 backwashing is likely to leave air bubbles in the lumens of the membranes
10 in sufficient amount to interfere with the integrity test.

3. The outside of the membranes 10 are exposed to air by opening a
drain valve 62 connected to a drain 64 to at least partially empty the tank 18.
The membranes 10 are not allowed, however, to dry out and their pores

10 remain wet. Where the tank 18 is periodically deconcentrated by draining it
and re-filling it with fresh feed water 12, the integrity test is preferably
performed during such a deconcentration to avoid the need for an additional
draining of the tank 18.

4. A transmembrane pressure is created across the membranes 1 0.
15 This is done by closing the outlet valve 28, opening the loop closure valves

42 and operating the permeate pump 26. This creates a suction in the
lumens of the membranes 10. The speed of the permeate pump 26 is
selected such that the suction is sufficient to draw an appreciable amount of
air through a defect of a relevant size according to calculations which are

20 known to those skilled in the art. The suction is not sufficient, however, to
overcome surface tension across the pores of the membranes 10 which
retains the permeate 14 in the lumens of the membranes 10 or exceed the
bubble point of a membrane 10 without defects. Typical transmembrane
pressures may range from 20 to 90 kPa. The preferred duration of this step

25 is selected with regard to the size of the collection vessel 34. At the end of
this step, the loop closure valves 42 are closed and the permeate pump 32
is stopped.

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5. Air is purged from the outside of the membranes 10 by closing the
drain valve 62 and opening the feed valve 32 to refill the tank 18.

6. Permeation is resumed at a low flux by opening the outlet valve 28
and operating the permeate pump 26 at an appropriate speed. Air that

5 passed through the membranes 10 is entrained with the flow of permeate
14 until it reaches the collection vessels 34. The air separates from the
permeate 14 in the collection vessels 34 and collects in them.

7. Permeation is stopped and pressures in the permeate collection
pipes 20 associated with the various membrane units 16 of the filtration

10 train 17 are allowed to equilibrate. With equal pressure in the permeate
collection pipes 22, the volume or air in one collection vessel 34 compared
to another is related to the integrity of the associated membrane units 16.

8. The volume, and optionally the pressure, of the air in each
collection vessel 34 is read and recorded manually or automatically.

15 9. Membrane units 16 associated with collection vessels 34 with

unacceptable amounts of air are isolated from the filtration train 17 by
closing their associated isolation valve 22.

10. Air in the collection vessel 34 is discharged by any of the
techniques described in step 2 above.

20 11. Regular permeation is resumed.

Steps 6 and 7 above increase the accuracy of the procedure but may
not be necessary in all systems. Particularly where a membrane unit 16
and its associated permeate collection pipes 20 are small, enough air may

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be collected in a portion step 4 alone to indicate a defect. If so, step 8 may
be replaced by measuring the volume of air collected during a selected
interval of time during step 4 while the membranes 10 are still subject to a
transmembrane pressure during step 4. The volume collected for a
5 membrane unit 16 may be converted to a volume at standard conditions
(assuming that the transmembrane pressure applied is reasonably
accurately known) or compared to air volumes collected from other
membrane units 16.

With collection vessels 34 associated with each membrane unit 16,

10 many membrane units 16 can be tested separately but simultaneously and
with a single recycle loop 40 and permeate pump 26. Preferably, a large
municipal or industrial filtration train 17 is divided into at least ten distinct
membrane units 16. In this way, if one of the membrane units 16 is found to
be defective there is at most a 10% drop in production of permeate 14 when

15 it is isolated from the filtration train. Further, it is preferable to make each
membrane unit 16 small enough that a defect of the relevant size is
distinguishable from diffusion. This preferred size limit varies for different
membranes 10 but typically corresponds with a capacity to produce a few
thousand m 3 /day of permeate 14 or about 6000 m 2 of membrane surface

20 area. Such membrane units 16 typically comprise a plurality of sub-units,
often referred to as modules. Various pipes typically connect permeate 14
collected from each sub-unit to the permeate collection pipes 20 serving the
entire membrane unit 16. These various pipes are preferably clear. In this
way, if a defective membrane unit 16 is identified, visual inspection of the

25 clear pipes during an integrity test is often sufficient to locate a defective
sub-unit within a membrane unit 16. Once identified, a defective membrane
unit 16 or sub-unit is isolated and either repaired or replaced.

The volume of air collected for each membrane unit 16 may be

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interpreted directly to indicate the presence or size of a defect using
calculations known to those skilled in the art. Alternatively or additionally,
the volume of air collected relating to one membrane unit 16 can be
compared to the volume of air collected from another membrane unit 16 or,
5 preferably, from several other membrane units 16. Provided that the
pressure in the various the collection vessels 34 is constant, there is no
need to know the pressure as is required to perform calculations relating
the volume collected to the presence or size of defects.

Now referring to Figures 3, an embodiment of the invention is shown
10 in which a plurality of membranes 10 (typically thousands) are assembled
into a shelled second membrane unit 116. To avoid repetition, process
steps or components will not be described specifically with reference to
Figure 3 where they are similar to process steps or components discussed
with reference to Figures 1 and 2 or generally known. Further, names and
15 numbers identifying components in the embodiment of Figures 1 and 2 may
be used for similar components in the following description of the
embodiment of Figure 3. For example, only a single second membrane unit
116 is shown in Figure 3 whereas each such second membrane unit 116
typically comprises several sub-units and a plurality of second membrane
20 units 116 are typically connected together into a filtration train in a manner
analogous to that shown in Figure 2.

During permeation, a feed pump 70 pumps feed water 12 through a
second feed valve 132 into the second membrane unit 116. Permeation is
performed in O/l mode by operating the feed pump 70 to create a positive
25 pressure on the outside of the membranes 10. Permeate 14 is produced in
the lumens of the membranes under some residual pressure and flows to
permeate collection pipes 20. Feed water 12 which does not pass through
the membranes 10 exits the second membrane module 116 through a

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recycle line 72 and may be returned to a feed supply 74, or to a recycle drain
76 through a recycle drain valve 78 or partially to both.

A second air collector 133 is provided at the top of the second
membrane unit 116 or at a high point in the permeate collection pipes 20
5 such that air entrained in permeate 14 will collect in the second air collector
133. The second air collector 133 has a collection vessel 34 and a solenoid
valve 136. The bottom of the collection vessel 34 is in fluid communication
with the flow of permeate 14. The solenoid valve 136 is operable to open
the top of the collection vessel 34 to atmosphere and many other types of
10 valves could also be suitable. Also provided is an air source 80, an air inlet
valve 82, a secondary drain 84, a secondary drain valve 86 and a vent valve
88. The air source 80 is operable to provide pressurized air (typically,
instrument air) and, although not shown, preferably services several second
membrane units 116.

15 To perform an integrity test, the steps described below are

performed. As above, steps 6 and 7 may be optional for some systems.

1. Any air in the collection vessel 34 is discharged by opening the
solenoid valve 136 briefly during permeation.

2. Permeation is stopped by stopping the feed pump 70 and closing
20 the second feed valve 132.

3. The outside of the membranes 10 are exposed to air by opening
secondary drain valve 86 and operating air source 80 to flow water in the
second membrane unit 116 out the secondary drain 84. While the term air
is used in this description, other gases, for example nitrogen, can also be

25 used. This step may also be performed without a secondary drain 84 by

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operating air source 80 to force feed water 12 in the second membrane unit
116 through the membranes 10.

4. A transmembrane pressure is created across the membranes 10.
This is done by closing secondary drain valve 86 and operating air source

5 80 to provide air at a selected pressure in the second membrane unit 116.

5. Air is purged from the outside of the membranes 10 by opening
vent valve 88 and second feed valve 132 and operating feed pump 70 to re-
fill the second membrane unit.

6. Permeation is resumed at a low flux by closing the vent valve 88
10 and operating the feed pump 70 at a reduced speed.

7. Permeation is stopped and pressures across the various second
membrane units 116 of a filtration train are allowed to equilibrate.

8. The volume, and optionally the pressure, of the air in each
collection vessel 34 is read and recorded manually or automatically.

15 9. Second membrane units 116 associated with collection vessels

34 with unacceptable amounts of air are isolated from a filtration train by
closing their associated isolation valve 22.

10. Regular permeation is resumed.

11. Air in the collection vessel 34 is discharged by opening the
20 solenoid valve 136.

It will be apparent to those skilled in the art that the equipment and

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methods described above can be adapted to other sorts of membranes and
other configurations of membrane units. In doing so, the inventors caution
that some adaptations are preferably used only when the membranes 10
have symmetrical pores. With reference to Figures 4, 5 and 6, the rate of
5 diffusion of air 90 through water 93 in the pores 92 of the membranes 10
increases as the length of the path of diffusion 94 decreases. Figure 4
illustrates a symmetrical pore 92. The path of diffusion 94 extends from a
meniscus 96 of the water 93 to the other side of the membrane 10
regardless of which side of the membrane 10 is the air 90 side. In Figure 5,

10 the membrane 10 has an asymmetrical pore 92 with the smaller side of the
pore 92 meeting the air 90. As the transmembrane pressure is applied
from air 90 side to water 93 side, a meniscus 96 forms on the air 90 side of
the membrane and the path of diffusion 94 again extends substantially
across the membrane 10. In Figure 6, however, the membrane 10 has an

15 asymmetrical pore 92 with the smaller side of the pore 92 meeting the water
93. As the transmembrane pressure is applied from air 90 side to the water
93 side, a meniscus 96 forms at a point inside the pore 92 where the
surface tension of the meniscus 96 balances the transmembrane pressure.
Typically, the path of diffusion 94 extends only part of the way across the

20 membrane 10. Returning to Figures 1 through 3, with asymmetric hollow
fibre membranes 10, the pores typically widen along a path from the
outsides of the membranes 10 to their lumens. When the transmembrane
pressure in the integrity test is applied from the feed side of the membranes
10 to the permeate side of the membranes 10 by either of the methods

25 described in relation to Figures 1 and 2 or 3, the situation is as shown in
Figures 4 or 5. In developing alternate embodiments, the situation shown in
Figure 6 is preferably avoided or the maximum size of a membrane unit
reduced from the values suggested above to compensate for the increased
rate of diffusion.

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Example

A pilot plant was constructed generally as shown in Figures 1 and 2
but using four membrane units each made of horizontal asymmetric hollow
fibre membranes having a total of 9 m 2 of surface area. Three of the four

5 membrane units were purposely made defective as described in the table
below. The fourth had no defects. The cleaning regimen for the membrane
unit included backwashing it once a day with a chemical cleaner into an
empty tank. While the tank was empty for cleaning, an integrity test was
performed generally as described above. Transmembrane pressure for the

10 test was set at three different values (as shown in the table below) and
maintained within 5% of the values given below by using a feedback signal
from a pressure transducer to a control valve on the discharge side of the
permeate pump. Air was collected for ten minutes and the height of the air
column collected in the collection vessel was measured with a capacitance

15 level probe while the system was still under suction. The air collection
vessel has a 25 mm diameter tube but the inventors believe that a 50 mm
diameter tube would have provided good resolution while providing more
space for the level probe.

The pressure and temperature at the time of the height reading were
20 recorded and, in combination with the cross sectional area of the collection
vessel, allowed the height readings to be converted to an air volumes at
standard conditions, which air volumes are given in the table below.

WO 01/45829 PCT/CA00/01461

-18-

Transmem-

hranp

LH at IC

Pressure
(kPa)

Volume for

Unit #1 -

Ul 111 TT 1

One cut fibre

Volume for

1 Init HO
unit itc. -

Two pin

holes in one

fibre

Volume for

One pin hole
in one fibre

Volume for

1 Init HA .

No defects

9ft

4R90 ml

AOO ml
HUU (TIL

icn ml
I OU 1 1 1 L_

n ml

55

Volume too
high to
measure
accurately

No data

280 mL

0 mL

62

Volume too
high to
measure
accurately

No data

350 mL

0 mL

In the trial at 62 kPa, no air was collected from Unit #4 after over
twenty minutes of suction. This result suggests that the testing method of
the present invention should be sufficiently sensitive to detect a single
5 broken fibre or pin hole in a large commercial membrane unit typically
having about 6,300 m 2 of surface area. In contrast, the same four
membrane units were tested with a pressure decay test using pressurized
air in the lumens of the fibres. At a transmembrane pressure of 55 kPa, for
example, the pressure drop over two minutes was about 0.5 kPa for unit #4
10 with no defects. The pressure drop for unit #1 with a cut fibre was about 47
kPa. Using this value as a basis for calculations, the pressure drop for a
single cut fibre in a 6,300 m 2 membrane unit would be only 0.02 kPa which
would be difficult to detect against the pressure drop caused by movement
of air through the wet pores of the membranes.

WO 01/45829

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PCT/CA00/01461

While preferred embodiments of the present invention have been
described, the embodiments disclosed are illustrative and not restrictive,
and the invention is intended to be defined by the appended claims.

WO 01/45829

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PCT/CA00/01461

CLAIMS

We claim:

1. A method of testing the integrity of membranes used to filter a liquid
feed applied to a first side of the membranes to produce a liquid permeate
5 at a second side of the membranes comprising the steps of:

a) dividing the membranes into one or more membrane units, each
membrane unit being of such a size that a defect of interest is
distinguishable from diffusion of air through the pores of the membranes in
the membrane unit; and,
10 b) for each membrane unit to be tested:

i) stopping filtration through the membrane unit;

ii) exposing the first side of the membranes in the membrane
unit to air;

15

iii) keeping the second side of the membranes exposed to the
liquid permeate;

20

iii) creating a transmembrane pressure across the
membranes from the first side of the membranes to the
second side of the membranes for a selected period of time,
the transmembrane pressure being sufficient to pass air into
the liquid permeate through a potential defect of concern in the
membranes but not sufficient to exceed the bubble point of a
membranes without defects;

25

iv) separating from the liquid permeate and collecting air
passing through the membrane unit during at least a part of
step b) iii) above;

v) measuring the volume of air collected in step b) iv) above;
and,

vi) interpreting whether the measured volume of air indicates

WO 01/45829

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PCT/CA00/01461

that there is a defect in the membranes of the membrane unit.

2. The method of claim 1 further comprising the steps of re-applying
feed to the first side of the membranes and resuming permeation at low flux
for a period of time after step b)iii and before measuring the volume of air

5 collected.

3. The method of claim 1 or 2 wherein air is collected individually from a
plurality of membrane units all subjected simultaneously to the same
transmembrane pressure, the pressure of the liquid permeate is
equilibrated across of the plurality of membrane units and the step of

10 interpreting whether a measured volume of air from a first membrane unit
indicates that there is a defect in the first membrane unit includes
comparing the measured volume of air from the first membrane unit to a
measured volume of air from another membrane unit.

4. The method of claim 1 wherein the air is applied to a feed side of
15 hollow fibre membranes normally operated in an O/l mode.

5. The method of claim 4 wherein the membranes have asymmetrical
pores which widen towards the lumens of the membranes.

6. The method of any of claims 1 - 5 wherein the membranes are
normally immersed during filtration in an open tank and operated in an O/l

20 mode, the first side of the membranes is exposed to air by draining the tank
and the transmembrane pressure is applied by applying a suction to the
liquid permeate.

7. The method of claim 6 wherein the step of exposing the first side of
the membranes to air by draining the tank coincides with a time in a filtration

WO 01/45829

-22-

PCT/CA00/01461

cycle at which the tank is drained to deconcentrate its contents where the
tank is drained to deconcentrate its contents is done at least as frequently
as the membranes are tested.

8. The method of claim 6 wherein the step of exposing the first side of
5 the membranes to air by draining the tank coincides with a time in a filtration

cycle at which the tank is drained to clean the membranes, where such
cleaning is done at least as frequently as the membranes are tested.

9. In a filtration system comprising;

(a) a tank for holding water to be filtered;
10 (b) an inlet for feed water into the tank;

(c) hollow fibre membranes normally immersed during permeation,
the outsides of the membranes in communication the water in the tank;

(d) a source of transmembrane pressure across the membranes for
removing a filtered permeate from the tank; and,

15 (e) an outlet for retentate from the tank;

the improvement comprising,

(i) a source of suction on a permeate collection pipe in fluid
communication with the lumens of a set of membranes operable without
producing permeate to produce a vacuum greater than the bubble point of a

20 defect in the membranes; and

(ii) an air collector in fluid communication with a high point in the
permeate collection pipe and operable to collect and release air that
passes from the outside of the set of membranes to the permeate collection
pipe and which permits the volume of air collected to be measured,

25 wherein the set of membranes is chosen to produce a membrane

unit of such a size that a defect of interest is distinguishable from diffusion
of air through the pores of the membranes in the membrane unit.

WO 01/45829

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PCT/CA00/01461

10. The system of claim 9 having a single source of suction operable
without producing permeate connected to a plurality of membrane units and
a plurality of air collectors, at least one associated with each membrane
unit.

5 11. In a filtration system comprising;

(a) a tank for holding water to be filtered;

(b) an inlet for feed water into the tank;

(c) a membrane unit of hollow fibre membranes normally immersed
during permeation, the outsides of the membranes in communication the

10 water in the tank;

(d) a source of transmembrane pressure across the membranes for
removing a filtered permeate from the tank; and,

(e) an outlet for retentate from the tank;
the improvement comprising,

15 (i) a source of pressure on the outside of the membranes operable in

the absence of water on the outside of a set of membranes operable to
produce a pressure greater than the bubble point of a defect; and

(ii) an air collector in fluid communication with a high point in a
permeate collection pipe and to collect any air that passes from the outside

20 of the set of the membranes to the permeate collection pipe and which
permits the volume of air collected to be measured,

wherein the set of membranes is chosen to produce a membrane
unit of such a size that a defect of interest is distinguishable from diffusion
of air through the pores of the membranes in the membrane unit.

25 12. The system of claim 11 having a single source of pressure on the
outside of the membranes operable in the absence of water on the outside
of the membranes connected to a plurality of membrane units and a plurality
of air collectors, at least one associated with each membrane unit.

SUBSTITUTE SHEET (RULE 26)

WO 01/45829

PCT/CA00/01461

SUBSTITUTE SHEET (RULE 26)

WO 01/45829

PCT/CAO0/01461

3/4

SUBSTITUTE SHEET (RULE 26)

WO 01/45829

PCT/CA00/01461

SUBSTITUTE SHEET (RULE 26)

INTERNATIONAL SEARCH REPORT

Inte ional Application No

PCT/CA 00/01461

A. CLASSIFICATION OF SUBJECT MATTE H

IPC 7 B01D65/10 G01N15/08

According to Inlemalional Patent Classification (IPC) or to both national classification and IPC

B. FIELDS SEARCHED

Minimum documentation searched (classification system followed by classification symbols)

IPC 7 B01D G01N

Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched

Electronic data base consulted during the international search (name of data base and, where practical, search terms used)

WPI Data, PAJ, EPO-Internal

C. DOCUMENTS CONSIDERED TO BE RELEVANT

Category 0 Citation of document, with indication, where appropriate, of the relevant passages

Relevant to claim No.

6B 2 132 366 A (BRUNSWICK CORPORATION)
4 Ouly 1984 (1984-07-04)
page 1, line 24-35; claims

WO 97 45193 A (0TV OMNIUM DE TRAITEHENTS
ET DE VALORISATION)
4 December 1997 (1997-12-04)
cited 1n the application
claims; figures

EP 0 139 202 A (FUJISAWA PHARMACEUTICAL
CO., LTD.) 2 May 1985 (1985-05-02)
claims

_/-

1-12

1-12

1-12

Further documents are listed in the continuation of box C

m

Patent family members are listed in annex.

• Special calegories of cited documents :

'A* document defining the general state of the art which is not

considered to be of particular relevance
•E f earlier document but published on or after the international

filing date

•L* document which may throw doubts on priority cfaim(s) or
which is cited to establish the publication date of another
citation or other special reason (as specified)

"O" document referring to an oral disclosure, use, exhibition or
other means

*P* document published prior to the international filing date but
later than the priority date claimed

*T* later document published after the international filing date
or priority date and not in conflict with the application but
cited to understand the principle or theory underlying the
invention

'X* document of particular relevance: the claimed invention
cannot be considered novel or cannot be considered to
involve an inventive step when the document is taken alone

■Y' document of particular relevance; the claimed invention

cannot be considered to involve an inventive step when the
document is combined with one or more other such docu-
ments, such combination being obvious to a person skilled
in the art.

document member of the same palent family

Date of the actual completion of the international search

28 February 2001

Date of mailing ol the international search report

06/03/2001

Name and mailing address of the ISA

European Patent Office. P.B. 5818 Patenttaan 2
NL - 2280 HV Rijswijk
Tel. (+31-70) 340-2040. Tx. 31 651 epo nl.
Fax: (+31-70) 340-3016

Authorized officer

Cordero Alvarez, M

Form PCT/ISA/210 (second sheet) (July 1992)

pagel of 2

INTERNATIONAL SEARCH REPORT —

Inte .onal Application No |

PCT/CA 00/01461

C.(Contlnuation) DOCUMENTS CONSIDERED TO BE RELEVANT

Category °

Citation of document, with indication.where appropriate, of the relevant passages

Relevant to claim No.

A

EP 0 592 066 A (MEMTEC JAPAN LIMITED)
13 April 1994 (1994-04-13)
cited in the application

claims
& US 5 353 630 A

11 October 1994 (1994-10-11)
cited in the application

l

Form PCT/ISA/210 (continuation of second sheet) (July 1992)

page- 2 of -2

INTERNATIONAL SEARCH REPORT

information on patent family members

Inte ronal Application No

PCT/CA 00/01461

Patent document

Publication

Patent family

Publication

cited in search report

date

member(s)

date

6B 2132366 A

04-07-1984

DE

3248185 A

05-07-1984

DE

3331419 A

14-03-1985

DE

3331420 A

14-03-1985

CA

1220047 A

07-04-1987

US

4614109 A

30-09-1986

WO 9745193 A

04-12-1997

FR

2749190 A

05-12-1997

AT

198165 T

15-01-2001

AU

718839 B

20-04-2000

AU

3096997 A

05-01-1998

BR

9709279 A

10-08-1999

DE

69703740 D

25-01-2001

EP

0909210 A

21-04-1999

HU

9902297 A

29-11-1999

JP

2000510766 T

22-08-2000

PL

330192 A

26-04-1999

EP

139202

A

02-

-05-1985

JP

1874038 C

26-09-1994

JP

5085207 B

06-12-1993

JP

60197287 A

05-10-1985

JP

1642519 C

28-02-1992

JP

2051135 B

06-11-1990

JP

60058530 A

04-04-1985

AT

42145 T

15-04-1989

DE

3477691 D

18-05-1989

US

4872974 A

10-10-1989

US

5064529 A

12-11-1991

EP

592066

A

13-

-04-1994

DE

69313574 D

09-10-1997

DE

69313574 T

08-01-1998

JP

2945988 B

06-09-1999

JP

6043089 A

18-02-1994

US

5353630 A

11-10-1994

Form PCT/JSA/210 {palent family annex) (July 1992)